Our goal is to determine the mechanism of abnormal brain function in severe liver disease. Toward this end we have two approaches: 1) to identify and isolate potentially toxic agents in the blood and spinal fluid of patients with hepatic coma, and 2) to examine the enzymes and substrates involved in cerebral ammonia metabolism in rats made acutely and chronically hyperammonemic. Cerebrospinal fluid of patients with demonstrated liver disease will be analyzed for concentrations of ammonia, glutamine, gamma-aminobutyrate, and alpha-keto-glutaramate (alpha-KGM). Particular attention will be devoted to establishing whether or not alpha-KGM levels in CSF a) are diagnostic of hepatic encephalopathy, b) correlate with the severity of neurological impairment, and c) when elevated, can exert a direct toxic action on the brain. Activities of the principal enzymes involved in the metabolism of ammonia-glutamine-alpha-ketoglutaramate (i.e., glutamic dehydrogenase, glutamine synthetase, glutamine transaminase, and alpha-amidase) will be determined in post-mortem brain samples of hepatic and non-hepatic patients, and attempts will be made to purify the alpha-amidase from human brain. As an experimental model of chronic hyperammonemia, rats will be prepared with a portacaval shunt and at intervals post-shunting they will be given an ammonia load to precipitate an "hepatic crisis". Brains of treated and control rats will be analyzed for concentrations of high-energy compounds, amino acids and ammonia, or examined histologically for presence of Alzheimer's glial cells. In addition, shunted rats will be made hypoglycemic and/or acutely hypoxic to test whether such metabolic stresses potentiate the toxicity of ammonia on the brain. BIBLIOGRAPHIC REFERENCES: Plum, F., and Hindfelt, B.: The neurological complications of liver disease. In metabolic and deficiency diseases of the nervous system. Handbook of Clinical Neurology, Vol. 31, Vinken, P.J., and Bruyn, G.W. (Eds.). North-Holland: Amsterdam. In press. 1976. Duffy, T.E., and Plum, F.: Seizures and comatose states. In Basic Neurochemistry, 2nd Edition. Albers, R.W., Siegel, G.J., Katzman, R., and Agranoff, B.W. (Eds.), Little, Brown: Boston. In press, 1976.